Start with good switches. I use nothing but the PCS SmartSwitch but the Switchlinc switches have improved recently and seem to be a good option as well. Not only do good switches work better but they look and feel much better just like good bathroom or lighting fixtures look and feel better than cheaper fixtures. Any of the switches can be combined with a matching slave switch for a 3-way circuit.
Definitely get switches that support scenes. All of the PCS switches support scenes. The Switchlinc switches have different versions of each type of switch so each type has a version which supports scenes.
A scene is simple when you see it, not so simple when you read about it. A scene capable switch can learn more than one X10 address. It will have it's primary address (i.e. A1), that you use just like any other X10 device, but it will also have the ability to respond to additional addresses as well (i.e. H1, H2, H3, etc.). Those additional addressed respond a little differently than a primary address. Instead of turning on when it received an H1 Hon command a switch which has H1 as a scene address will ramp towards a pre-programmed dim level at a pre-programmed ramp rate. A living room lamp might know scene H1 as 20% intensity with a 3 second ramp rate, scene H2 as 50%/3sec, H3 as 100%/3sec, and H4 as 0%(off)/9min. Other lights in the living room would know each of those scenes differently but they would be designed to all work together. The real power of scenes is that one X10 command, i.e. H1 Hon, will cause a number of lights to simultaneously ramp towards a predetermined scene. In this case H1 might be for TV watching, H2 for reading, H3 for clean up and H4 for "goodnight".
If you're using scenes, I'd suggest the straight IR543 for control from your remote. It's cheap, responds instantly and is quite capable of initiating the scenes you'd need to initiate from a single room. Just devote one house code to scenes and you're set. The Ocelot is good to have as an intelligent, programmable controller (i.e. controls outside lights based on sunset/sunrise, handles your home/away/vacation logic, etc.) but it's not as good for simply translating commands from IR to X10 for a number of reasons including that it translates relatively slowly. You won't need the Ocelot at first but you'll probably want to add it later as your system grows beyond the home theater's room.
One other control point that I would suggest is the in-wall keypad transmitters. There are nice versions made by PCS, Switchlinc, and ACT. They go in the wall just like wall switch except they have a series of buttons on them which transmit X10. You program these to transmit your scene commands so that one button on the wall will initiate the appropriate scenes.
For all of this stuff I'd recommend
http://www.homeautomationnet.com/ They have prices as low as anybody (much lower than many) and excellent support. The owner, Bill E., is often seen posting in this forum.
